ausblenden:
Schlagwörter:
Adsorption isotherms; adsorption kinetics; aromatics; platinum; surface chemical reaction; ultraviolet photoelectron spectroscopy; X-ray photoelectron spectroscopy
19: Iron oxide model catalysts: adsorption & catalysis
Zusammenfassung:
The interaction of ethylbenzene (EB) and styrene with Pt(111) was studied by UPS and XPS for
adsorption temperatures between 135 K and 870 K. Below 350 K, styrene chemisorbs strongly and the
work function decreases by more than 2 eV indicating strong polarization or charge trans-fer. This is
accompanied by different bonding shifts of the p and s orbitals towards smaller binding energy. After
saturation of the chemisorbed layer, physisorption and finally condensation in form of clusters is
observed. The isosteric heats of adsorption for physisorbed and condensed styrene are 61 kJ/mol and
58.5 kJ/mol, respectively. The first EB layer dissociates into chemisorbed styrene and hydrogen atoms.
The following physisorbed and condensed layers consist of undissociated EB. Upon annealing in EB or
styrene atmosphere, chemisorbed gamma-styrene polymerizes at about 400 K with a saturation coverage
slightly above one monolayer. Upon further annealing the layer starts to decompose and beyond 700 K
it forms a graphitic coke layer. Annealing of a gamma-styrene layer without further gas admission yields the
same species but with lower coverage
